Viscosity modifier polybutadiene polymers

ABSTRACT

The present invention relates to hydrogenated polybutadiene comprising monomeric units of 1,4-butadiene and 1,2-butadiene addition products. The copolymer is hydrogenated and comprises at least 10% by weight of at least one crystallizable segment and at least one low crystallinity segment.

This is a divisional of application Ser. No. 08/380,488, filed Jan. 30,1995, now abandoned, which is a continuation of application Ser. No.08/226,578 filed Apr. 12, 1994 now abandoned, which is a divisional ofapplication Ser. No. 670,114, filed Mar. 15, 1991 now U.S. Pat. No.5,310,814 granted May 10, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydrogenated polybutadiene comprisingmonomeric units of 1,4-butadiene and 1,2-butadiene addition products.More particularly, it relates to polybutadiene comprising hydrogenatedblocks or segments of monomeric units of 1,2-butadiene and 1,4-butadieneaddition products containing at least one crystallizable segment orblock comprising an average of at least about 10 weight percent of thetotal hydrogenated copolymer chain, and at least one low crystallinitysegment or block. The instant invention also relates to oleaginouscompositions containing said copolymers as viscosity index improveradditives, a process for making these copolymers and a method to controlthe viscosity of oleaginous compositions.

2. Description Of Related Art

Various copolymers of butadiene with other olefins are known to be usedas oil additives. These include hydrogenated copolymers of butadienewith another conjugated diene such as isoprene. The copolymers aredisclosed to be random or block copolymers. The following review of therelated art illustrates attempts which have been made to develophydrogenated butadiene base copolymers for use as an oil additiveincluding a viscosity modifier.

U.S. Pat. No. 4,804,794 discloses segmented copolymers of ethylene andat least one other α-olefin monomer. Each copolymer is intramolecularlyheterogeneous and intramolecularly homogeneous. At least one segment ofthe copolymer constituting at least 10% of the copolymer chain, is acrystallizable segment. The remaining segments of the copolymer chainare termed low crystallinity segments, and are characterized by anethylene content of not greater than about 53 weight percent.

The α-olefin can include those containing 3 to 18 carbon atoms.α-olefins having 3 to 6 carbon atoms are indicated to be preferred. Withthe most preferred copolymers being copolymers of ethylene withpropylene or ethylene with propylene and diene. The copolymers aredisclosed to improve the properties in oleaginous fluids, in particularlubricating oil.

U.S. Pat. No. 3,419,365 discloses hydrogenated copolymers of butadieneand styrene as pour point depressants for distillate fuel oil; U.S. Pat.No. 3,393,057 discloses polymers of butadiene C10 to C24 normalalpha-monoolefins and styrene or indene as pour point depressants forfuel and lubricating oils; and U.S. Pat. No. 3,635,685 discloses pourpoint depressants comprising hydrogenated butadiene-styrene copolymerswhich contain a hydroxy, carboxy, or pyridyl terminal group.

U.S. Pat. No. 3,312,621 discloses polymers of conjugated diolefins whichare predominantly in the 1,4-addition configuration, as viscosity index(V.I.) improvers. Butadiene, isoprene, 1,3-pentadiene, and copolymers ofsuch diolefins are specifically disclosed as suitable.

U.S. Pat. No. 3,600,311 discloses viscosity index improvers ofhydrogenated homopolymers of butadiene in which about 45 to 95 % of thebutadiene monomers are in the 1,4-configuration.

U.S. Pat. No. 3,795,615 discloses viscosity index improvers ofhydrogenated copolymers of butadiene with a different conjugated diene,e.g., isoprene in which the monomer units in the polymer arepredominantly in the 1,4-configuration. This patent discloses thathydrogenated 1,4-polybutadiene is not useful as a viscosity indeximprover, since the final product is an oil-insoluble polyethylene.Hydrogenated polybutadienes with an appropriate amount of 1,2-structurewould give the necessary solubility and would have viscosity indeximproving properties. However, this references teaches that it isnecessary to very precisely control the amount of 1,2-structure formed.If an inadequate amount of 1,2-structure is formed, the polymer is notsufficiently soluble; if too much 1,2-structure is formed, the polymeris not as effective in increasing the viscosity index. The patentfurther discloses that when polybutadiene is anionically polymerized tothe high degree of polymerization needed for viscosity index improvers ,it is very difficult to obtain precise control of the amount of1,2-addition product by variations in reaction conditions.

U.S. Pat. No. 3,965,019 discloses hydrogenated random, tapered or blockcopolymers of butadiene and isoprene to be useful as viscositymodifiers.

U.S. Pat. No. 4,032,459 discloses a viscosity index improver comprisinga copolymer of butadiene and isoprene having between 20-55%1,4-configuration, this polymer then having been hydrogenated to removesubstantially all of the olefinic unsaturation.

U.S. Pat. No. 4,073,737 discloses viscosity index improver comprised ofa hydrogenated copolymer produced by copolymerization of from about 1 toabout 10 mole percent butadiene, at least one other C5 to C12 conjugateddiene, and up to 45 mole percent of a vinyl aromatic monomer.

A useful class of viscosity index improvers for lube oil compositionsare star-shaped polymers comprising a nucleus such as divinylbenzenewith polymeric arms linked to it. Such polymers are disclosed inpatents, such as U.S. Pat. No. 4,358,565 and 4,620,048. Generallystar-shaped polymers are disclosed to be formed by polymerizing one ormore conjugated dienes and optionally, one or more monoalkenylarenecompound in solution in the presence of an ionic initiator to form aliving polymer. For the purpose of the present invention the term"living polymer" is used consistent with Billmeyer, Textbook of PolymerScience, 2d Ed., page 348, Wiley-Interscience, John Wiley and Sons, page318 (1971). Specific conjugated dienes include conjugated dienes having4 to 12 carbon atoms and optionally, one or more monoalkenylarenecompounds. Typical and useful conjugated dienes include butadiene(1,3-butadiene) and isoprene. The living polymers thereby produced arethen reacted with a polyalkenyl coupling agent to form star-shapedpolymers. The coupling agents have at least two non-conjugated alkenylgroups. The groups are usually attached to the same or differentelectron drawing groups, e.g., an aromatic nucleus. Such compounds havethe property that at least two of the alkenyl groups are capable ofindependent reaction with different living polymers, and in thisrespect, are different from conventional dienes polymerizable monomers,such as butadiene and isoprene. The coupling agents may be aliphatic,aromatic or heterocyclic. Examples of aliphatic compounds includepolyvinyl and polyallyl acetylenes, diacetylenes, phosphates, andphosphites, as well as the dimethacrylates, e.g., ethyl dimethacrylate.Examples of suitable heterocyclic compounds include divinyl pyridine anddivinyl thiophene. Coupling agents disclosed to be preferred in the U.S.Pat. No. 4,358,565 patent are polyalkenyl aromatic compounds with themost preferred being indicated to be polyvinyl aromatic compounds.Examples of such compounds include those aromatic compounds, e.g.,benzene, toluene, xylene, anthracene, naphthalene, and durene which aresubstituted by at least two alkenyl groups, preferably directly attachedthereto. Specific examples include polyvinyl benzenes, e.g., divinyl,trivinyl, and tetravinyl benzenes; divinyl, trivinyl and tetravinyl,autho, meta and paraxylenes, divinyl naphthalene, divinyl ethyl benzene,divinyl biphenyl, diisobutenyl benzene, diisopropanol benzene, anddiisopropanol biphenyl. The polyalkenyl coupling agent should be addedto the living polymer after the polymerization of the monomers issubstantially complete, i.e., the agent should only be added aftersubstantially all of the monomer has been converted to living polymer.

The amount of polyalkenyl coupling agent added may vary, but preferably,at least 0.5 moles is used per mole of unsaturated living polymer.Amounts from 1 to 15 moles, and preferably 1.5 to 5 moles are preferred.

There exists a need for viscosity index improvers which, when added tooleaginous compositions, such as lube oil compositions, yieldcompositions exhibiting better or improved low temperature viscometriccharacteristics than are obtainable by the use of conventional viscosityindex improver additives. The copolymers of the instant inventionprovide oleaginous compositions exhibiting such improved low temperatureviscometric characteristics, and additionally, improved shear stability.

For convenience, certain terms that are repeated throughout the presentspecification and claims are defined below.

a. Viscosity Index (V.I.) is the ability of a lubricating oil toaccommodate increase in temperature with a minimum decrease inviscosity. The greater this ability, the higher the V.I.

b. A block copolymer is a copolymer having at least one sequence (alsoreferred to as block or segment) of the same monomer units. Eachsequence has at least two monomer units. Block copolymers typically havea plurality of each type of monomer making up the copolymer. The termsrelating to block copolymer are consistent with those given inBillmeyer, Jr., Textbook of Polymer Science, Second Edition,Wiley-Interscience (1971). For the purpose of the present invention theterm block or segmented copolymer includes a copolymer comprisingmonomeric units of 1,2-butadiene and 1,4-butadiene.

c. Average methylene content of a segment of the hydrogenated copolymeris the average number of methylene moieties or units present in thesegment. The methylene units are those present in the particular segmentas a result of the polymerization and hydrogenation of butadiene and atleast one other conjugated diene, such as isoprene. Thus, for example,the hydrogenation product of the 1,4-addition product of two1,4-butadiene molecules contains one methylene segment comprised ofeight methylene units and has a methylene content of 100%, i.e.,--CH2--CH2--CH2--CH2--CH2--CH2--CH2--. The hydrogenation product of the1,2-addition product of 1,2-butadiene contains one methylene unitsalternating with an ethylene substituted methylene unit, i.e., ##STR1##

The following defines how percent methylene units are calculated fromthe percentages of hydrogenated 1,2 and 1,4 polybutadiene in thepolymer. Each enchained 1,4-butadiene (B₁,4) unit contributes fourmethylenes. Each 1,2-butadiene contributes one methylene and onesubstituted methylene. Where B represents the mole fraction1,4-butadiene then (1-B) is the fraction 1,2-butadiene. The molefraction methylenes present, X_(CH).sbsb.2 is then ##EQU1## where B₁,4is the fraction of 1,4-addition of butadiene. For B₁,4 =1, X_(CH).sbsb.2=1. For all 1,2-addition X_(CH).sbsb.2 =0.5, but there can be no longmethylene sequences.

To obtain crystallizable sequences there must be sequences of 1,4enchained units. For random addition of 1,2-butadiene and 1,4-butadieneunits B₁,4 is approximately 0.3 or 30 percent to obtain crystallinity.From formula (1) X_(CH).sbsb.2 =0.73 at B₁,4 =0.3. In principle, if thestatistical distribution of 1,2 and 1,4-butadiene additions is of ablock type, than random crystallinity could occur at B₁,4 below 0.3.

In all cases where sequences of methylenes are long enough tocrystallize at least two adjacent hydrogenated 1,4-butadiene units arepresent, and generally 3 or more are present. In such cases, methylenesfrom 1,2-butadiene becomes less important for crystallization since theyadd only one or two units to an 8 to 12 unit sequence. For purposes ofthe present invention the composition of crystallizable segments is interms of 1,4-butadiene content, i.e, only those methylene segmentscontributed by 1,4-butadiene units are counted

d. By "crystallize" it is meant that the methylene sequences in thepolymer associate into ordered state consistent with the classicaldefinition of polymer crystallinity as set forth, for example, by Flory,Principles of Polymer Chemistry, Cornell University Press (1953).

e. Crystallizable units are defined as methylene groups in sequencewhich exhibit a heat of fusion when measured by differential scanningcalorimetry (DSC) upon cooling from the melt. In a procedure useful forthe present invention a sample can be formed into an approximately 0.030inch thick sheet for 30 minutes at 150° C. and then annealed at 20° C.for 48 hours prior to measurement, loaded into the calorimeter at thattemperature, rapidly cooled to -100° C. and scanned to 150° C. at 20°C./minute. Only sequences melting between 20° C. and 140° C. areincluded.

f. The weight percent crystallizable units is: ##EQU2##

On this basis pure melt crystallized polymethylene of high Mw (i.e.,where the end groups effects are not significant; typically greaterequal or about 20,000) has about 60% crystallizable units. Kineticrestrictions prevent them from all crystallizing. Percent crystallinitycan be measured by a techniques, as defined in G. Ver Strate, Z. W.Wilchinsky, J. Pol. Sci. Physics, A2, 9, 127 (1971), which isincorporated herein by reference. The degree of crystallinity measuredis a function of the sample's annealing history. Some low amount isdesirable in this product when the sample is annealed at 20° C. for morethan 48 hours after preparation of a void-free, strain-free specimen byheating to 150 ° C. for 30 minutes in a suitable mold. Crystallizabilityalso depends on other factors: temperature, diluent, and the compositionof the copolymer.

g. The association temperature (T_(a)), is the temperature at whichcrystallization of the copolymer of the present invention can bedetermined by studying the temperature dependance of the relativeviscosity (πrel). Deviation from an established (dπrel/dT) trend occurswhen significant association at polymer segments due to crystallinitystarts. (ASTM method D-445 for kinematic viscosity can be run at aseries of temperatures. The polymer concentration in these measurementsshould be the same as that in the formulated oil, for example, 1%).

h. The cloud point temperature is the temperature (T_(c)) at whichcrystalline clouds (turbidity) are first observable upon cooling of oilwhen tested according to ASTM D-2500. The cloud paint temperature can becorrelated with the association temperature.

i. A crystallizable segment of the hydrogenated copolymer chain is richin methylene units, with an average methylene content of at least about75 mole percent. The methylene content depends on the monomers used toprepare the polymer and the nature of their inclusion in the polymer.The methylene units will crystallize at a given temperature andconcentration in solution only if they are in long enough sequences,with only a limited number of interruptions due to substituted methyleneunits. More interruptions are acceptable with methyl substitutions thanwith larger groups since methyl groups can enter the polymethylenecrystal lattice. Methylene units can be identified by C₁₃ NMR, T.Hayashi, Y. Iroue, R. Chujo, Macromolecules, 21, 3139, 1988, andreferences therein. Sequences of 5 or more cannot be distinguished.However units are actually crystallizable only if they are present insequences of about 13 methylenes or longer.

j. A low crystallinity segment has an average methylene content lessthan about 75 mole percent, and is characterized in the unoriented bulkstate after at least 24 hours annealing by a degree of crystallinity ofless than about 0.2% at 23° C.

k. Molecular weights of the hydrogenated copolymer were measured by acombination of gel permeation chromatography and on line laser lightscattering and described in G. Ver Strate, C. Cozewith, S. Ju,Macromolecules, 21, 3360, 1989. The specific refractive index incrementin trichlorobenzene at 135° C. was assumed to be -0,104 cc/g for allhydrocarbon structures.

SUMMARY OF THE INVENTION

The present invention is directed to a hydrogenated block copolymer, aprocess to make the copolymer, compositions containing the copolymer andmethods to use the copolymer.

The hydrogenated block copolymer of the preset invention comprises ahydrogenated block copolymer comprising monomeric units derived from1,4-butadiene and 1,2-butadiene addition products of the polymerizationof butadiene. The copolymer is hydrogenated and comprises at least 10weight percent by weight of at least one crystallizable segmentcomprised of methylene units. Correspondingly, the crystallizablesegment has an average 1,4-polybutadiene the content of at least about20 mole percent and preferably at least 30 mole percent. The blockcopolymer has at least one low crystallinity segment comprised ofmethylene units and substituted methylene units and has an average1,4-polybutadiene content of not greater than 20 mole percent andpreferably less than 10 mole percent. The 1,4-butadiene and1,2-butadiene units are present in amounts effective to provide at leastone crystallizable segment and at least one low crystallinity segment. Apreferred block copolymer is where the copolymer is in star copolymerform having from 4 to 25 and preferably 5 to 15 arms.

Preferably, the crystallizable segments have a number average molecularweight of at least 500. The average 1,4-polybutadiene content is atleast 20 mole percent and preferably at least 50 percent of themethylene units are connected in series of at least 13 adjacentmethylene units in length. The remaining segments of the copolymer chainare the low crystallinity segments preferably having an average1,4-polybutadiene content of less than about 20 mole percent.

The present invention includes compositions comprising oleaginouscompounds and the above recited hydrogenated block copolymer. Preferablythe oleaginous component is an oil composition comprising oil, such aslubricating oil. Typically, the oleaginous composition comprises from0.1 to 50, preferably from 0.05 to 25 percent by weight of thehydrogenated copolymer of the present invention. Preferred compositionsof the present invention comprise copolymer as recited above having acrystallization temperature (T_(a)) and oil having a cloud pointtemperature (T_(c)), where (T_(a)) is greater than (T_(c)). Thelubricating oil compositions can contain additional additives, such asother viscosity modifiers, ashless dispersants, antioxidants, corrosioninhibitors, detergents, pour point depressants, antiwear agents, and thelike.

The copolymers have been found to impart excellent low temperatureviscometric properties to oleaginous fluids, particularly lubricatingoils. The compositions have satisfactory viscosities at roomtemperatures and at higher temperatures. The compositions of the presentinvention are useful for typical lubricating oil compositions such asautomatic transmission fluids, heavy duty oil suitable for use incrankcases of gasoline and diesel engines, and any machinery containinggears and transmitting units.

The present invention additionally comprises a process to make thehydrogenated block copolymer recited above. The process comprises thesteps of polymerizing a precursor block copolymer comprising at leastone segment comprising at least 20 percent by mole of monomeric units of1,4-butadiene, and at least one comonomer segment comprising comonomerunits of 1,2-butadiene. The process further comprises substantiallyhydrogenating the precursor copolymer to form the above recitedhydrogenated block copolymer. The process is preferably an anionicpolymerization. In forming the precursor block copolymer thepolymerization process preferably takes either of two approaches. Thefirst is to first control the polymerization to form 1,4-butadienesegments, and then control the polymerization to form comonomer segmentscomprising at least 70, and preferably at least 75, and more preferablyat least 80 mole percent of 1,2-butadiene monomeric units.Alternatively, the comonomer can first be polymerized to form acomonomer segments comprising at least 70, preferably at least 75, andmore preferably at least 80 mole percent of 1,2-butadiene monomericunits. The polymerization is then controlled to form 1,4-butadienesegments. Upon completion of the polymerization of the 1,4-butadieneadditional comonomer can be added and the polymerization then controlledto form comonomer segments comprising at least 75 mole percent of1,2-butadiene monomeric units.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to hydrogenated block copolymers basedon butadiene comprising monomeric units derived from 1,4-butadiene and1,2-butadiene addition products. The copolymer contains at least onecrystallizable segment or block and at least one low crystallinitysegment or block. The hydrogenated copolymers are made by the controlledpolymerization of butadiene, preferably by addition polymerization. Thepolymerization results in a precursor block copolymer comprising atleast one 1,4-butadiene segment and at least one comonomer segmentcomprising comonomer units derived 1,2-butadiene, the copolymercomprising at least 10 percent by weight of the 1,4-butadiene segments.The precursor copolymer is then hydrogenated to substantially saturatethe olefinic bonds and to form a hydrogenated copolymer containing atleast one crystallizable segment and at least one low crystallinitysegment. The crystallizable segment comprises at least an average ofabout 10 weight percent of the hydrogenated copolymer chain and containsan average 1,4-polybutadiene content of at least about 20 mole percent,preferably at least about 30 mole percent. An adequate amount of themethylene units are joined in sequences containing at least about 13methylene units to permit crystallization.

The low crystallinity segment has an average 1,4-polybutadiene contentof less than 30 mole percent, preferably less than about 20 molepercent, and rich in substituted methylene units. The low-crystallinitysegment correspondingly contains an average of at least about 22 molepercent, more preferably at least about 24 mole percent substitutedmethylene units. The substituted methylene units from the 1,2-butadieneare represented by the formula ##STR2## wherein R is an ethyl group.

The low crystallinity segment can contain, in addition to thehydrogenated 1,2-addition butadiene comonomer, hydrogenated 1,4-additionbutadiene and minor amounts, i.e., from 0 to 5 mole percent, of otherconjugated diene polymerization products. Such other conjugated dienesinclude those having from 5 to 24 carbon atoms. Thus, for example, thelow crystallinity segment may contain the hydrogenated polymerizationproducts of 1,2-butadiene, i.e., poly-1,2-butadiene, 1,4-butadiene,i.e., hydrogenated poly-1,4-butadiene, and isoprene, i.e., hydrogenatedpolyisoprene.

The copolymer may also optimally contain up to 5 mole percent of thehydrogenated polymerization product of other monomers such as, forexample, monovinyl arenes such as styrene or substituted styrenemethacrylates, vinyl pyridines or other anionically polymerizablemonomers.

The size of the crystallizable segment which is present in thehydrogenated copolymer is in general dependent upon the relative amountsof 1,4-butadiene present in the precursor polymer. The crystallizablesegment comprises at least about 10 weight percent, preferably fromabout 10 to about 90 weight percent, more preferably from about 20 toabout 85 weight percent, and most preferably from about 40 to 65 weightpercent of the total hydrogenated copolymer chain. Correspondingly, theprecursor copolymer contains at least about 10 weight percent,preferably at least about 20 weight percent (e.g., from about 25 toabout 60), and more preferably at least about 35 weight percent of1,2-butadiene. Generally, the greater the amount of 1,4-butadienepresent in the precursor copolymer, the larger the crystallizablesegment in the hydrogenated copolymer.

In order to attain the preferred hydrogenated copolymer comprisingcopolymer chains containing at least one crystallizable segmentcomprised of methylene units and at least one low crystallinity segmentcomprised of methylene units and methylene units substituted with ethylgroups, the polymerization of the butadiene is controlled to control theamount of 1,2-butadiene which forms.

Not all of the 1,4-butadiene present in the precursor copolymer forms(upon hydrogenation) the crystallizable segment. Some of thehydrogenated 1,4-butadiene may be present in the low crystallinitysegment. Thus, for example, the low crystallinity segment may comprisethe hydrogenation products of 1,4-addition butadiene, and 1,2-additionbutadiene.

The crystallizable segment can also contain some of the hydrogenationproduct of 1,2-butadiene, provided the amounts of those otherhydrogenated moieties are insufficient to lower the average1,4-polybutadiene content of the crystallizable segment below about 20mole percent.

The copolymers are preferably produced by anionic polymerizationfollowed by hydrogenation. The hydrogenated reaction products of1,4-butadiene and 1,2-butadiene. The 1,4-configuration speciespredominate. The 1,2-addition of butadiene will yield a recurringstructure represented by the formula ##STR3##

Hydrogenation of this structure results in a structure represented bythe formula ##STR4##

Therefore, a hydrogenated copolymer of butadiene contains the followingspecies: ##STR5## obtained from the hydrogenation of 1,4-butadiene; and##STR6## obtained from the hydrogenation of 1,2-addition butadiene.

The recurring structural units other than those obtained by thehydrogenation of the 1,4-addition and 1,2-addition of butadiene may bepresent in both the crystallizable and low crystallinity segment. Ifthey are present in the crystallizable segment, however, they arepresent in amounts which are insufficient to affect the crystallizablecharacteristics of said segment.

The crystallizable segments or blocks present in the hydrogenatedcopolymer are comprised predominantly of methylene units which are,inter alia, provided by the hydrogenation of the 1,4-butadiene presentin the precursor copolymer. Thus, polymerizing butadiene monomer, i.e.,CH₂ ═CH--CH═CH₂, by 1,4-addition yields a precursor polymer segmentcontaining recurring structural unit of the formula ##STR7##

Hydrogenating this precursor polymer chain yields a polymer segmentcontaining the following recurring structural unit ##STR8## i.e.,containing only methylene units. This recurring structural unit,provided it is sufficiently long, e.g., contains at least about 13methylene units, forms the crystallizable segment of the polymer chain.

Thus, there are two requirements that must be fulfilled in order for asegment to be crystallizable. The first requirement is that the segmenthave an average 1,4-polybutadiene content of at least about 20 molepercent, preferably at least about 30 weight percent (e.g., from about20 to about 80 weight percent). The second is that the methylene unitsbe in sequences sufficiently long to impart crystallinity to saidsegment. Generally, these sequences are at least 13 methylenes orlonger, preferably at least 17 methylenes or longer, and more preferablyat least about 21 methylenes or longer.

In a preferred copolymer of the instant invention there is at leastabout 20 mole percent of the butadiene in the 1,4-configuration in theprecursor polymer. The precursor copolymer contains at least an amountof butadiene units in the 1,4-configuration sufficient to provide ahydrogenated copolymer containing at least one crystallizable segmentcomprising at least about 20 weight percent of said hydrogenatedcopolymer.

Polymerizing butadiene monomer by 1,2-addition and 1,4-addition yields aprecursor polymer chain containing the following recurring structuralunits ##STR9##

Hydrogenating this precursor polymer yields a hydrogenated polymer chaincontaining the following recurring structural units ##STR10##

Recurring structural unit Ia contains one methylene unit and asubstituted methylene unit, i.e., ##STR11##

Where there are relatively large amounts of these substituted methylenemoieties in a polymer segment, generally greater or equal to about 30mole percent, the resulting hydrogenated polymer segment is a lowcrystallinity segment. The segment containing at least about 20 molepercent 1,4-polybutadiene units, and if these methylene segments are ofsufficient length, is a crystallizable segment. ##STR12## derived fromthe hydrogenation of the 1,2-addition product of two moles of butadienefor every mole of 1,4-butadiene, will generally not be a crystallizablesegment because it is relatively rich in substituted methylene units,and the methylene sequences are not sufficiently long. A segmentcontaining the recurring structural unit ##STR13## derived from thehydrogenation of the 1,4-addition of two moles of butadiene for everymole of 1,2-butadiene, will be a crystallizable segment since itcontains at least 30 mole percent 1,4-polybutadiene units, and since itcontains uninterrupted methylene sequences containing at least about 13methylene units.

The copolymers of this invention will contain at least onecrystallizable segment rich in methylene units (hereinafter called an"M" segment) and at least one low crystallinity segment relatively richin substituted methylene units (hereinafter called a "T" segment). Thecopolymers may be therefore illustrated by copolymers selected from thegroup consisting of copolymer chain structures having the followingsegment sequences: ##STR14## wherein M and T are defined above, M₁ andM₂ can be the same or different and are each M segments, T₁, T₂ and T₃can be the same or different and are each T segments, and x is aninteger of from 0 to 3.

when x=0, the copolymer's M, i.e., M₂ segment is positioned between twoT segments, and the M segment can be positioned substantially in thecenter of the polymer chain (that is, the T₁ and T₃ segments can besubstantially the same molecular weight and the sum of the molecularweight of the T₁ and T₃ segments can be substantially equal to themolecular weight of the M2 segment), although this is not essential tothe practice of this invention. Preferably, the copolymer will containonly one M segment per chain. Therefore, structures III and IV (x=0) arepreferred, with structure II being more preferred.

The preferred copolymer chain structures, from the standpoint ofproviding oleaginous compositions such as lube oil compositions haveexcellent low temperature viscometric properties.

Preferably, the M segments and T segments of the copolymer are locatedalong the copolymer chain so that only a limited number of the copolymerchains can associate before the steric problems associated with packingthe low crystallinity T segments prevents further agglomeration.Therefore, in a preferred embodiment, the M segment is located near thecenter of the copolymer chain and only one M segment is in the chain. Inthe case where x is one or larger it is important that the T₁ and T₃segments be sufficiently large to prevent association of the M segmentsfrom different polymer chain.

Generally, copolymers of the structure

    M.sub.1 --(T--M.sub.2).sub.z                               (V)

wherein M₁, M₂ and T are as defined above, and wherein z is an integerof at least 1, are undesirable as viscosity modifier polymers. Solutionsof structure V copolymers in oil tend to gel even when the M and Tportions have exactly the same composition and molecular weight asstructure IV copolymers (with x=z=1). It is believed this poor viscositymodifier performance is due to the inability of a center T segment tosterically stabilize against association.

The M segments of the copolymers of this invention comprise the1,4-addition product of butadiene which has been hydrogenated, but canalso comprise at least one other hydrogenated diolefin monomer, providedthe 1,4-polybutadiene content of said M segment is at least about 30mole percent and a majority of the methylene sequences are sufficientlylong, e.g., contain at least about 13 methylene units. The T segmentscomprise a mixture of hydrogenated butadiene in the 1,2-configurationand the 1,4-configuration and have a 1,4-polybutadiene content notgreater than about 20 mole percent. The T and T₂ segments can containamounts of hydrogenated 1,4-configuration butadiene monomers, i.e.,1,4-polybutadiene units, provided the total methylene content of saidsegments does not exceed about 70 mole percent.

A preferred embodiment, a hydrogenated block or segmented copolymer of1,4-butadiene and 1,2-butadiene contains at least one crystallizableblock or segment and at least one non-crystallizable block or segment.Such block or segment copolymers may be represented by formula IVdescribed hereinbefore, i.e., T₁₋₋(M₁ --T₂)_(x) --M₂ --T₃ wherein M₁,M₂, T₁, T₂, T₃ and x are as defined hereinbefore. Preferably, M₁ and M₂are comprised predominantly or solely of methylene units derived fromthe polymerized 1,4-butadiene which has subsequently been hydrogenated.T₁ T₂ and T₃ contain adequate substituted methylenes to render thesegments of low crystallinity and may generally be derived, from1,2-polymerized butadiene which has been hydrogenated. In forming ablock copolymer of the structure T₁ --M₂ --T₃, butadiene is firstpolymerized to form 1,2-butadiene monomer units, to form a precursorcopolymer T₁ ' segment containing a recurring structure represented bythe formula ##STR15## wherein a is a number of at least 1. Uponhydrogenation this structure becomes ##STR16##

Upon complete or substantially complete polymerization merization by1,2-addition, butadiene monomer is reacted with the"living"1,2-butadiene segment. The butadiene is polymerized via1,4-addition (generally there may be some fraction of 1,2-butadieneaddition, although this may be kept to a minimum by appropriate reactionconditions), to form a precursor copolymer segment M' containing arecurring structure represented by the formula .paren open-st.CH₂ --CH=CH--CH₂ .paren close-st._(a) ',

wherein a' is a number of at least 1. Upon hydrogenation this structurebecomes (CH₂ --CH₂ --CH₂ --CH₂ .paren close-st._(a).

Upon completion or substantial completion of polymerization to by1,4-addition, the 1,2-addition reaction is resumed with the precursorblock copolymer T₁ '--M₂ '--, with M₂ ' being the "living" butadieneblock. The 1,2-addition polymerization is continued to form precursorcopolymer segment T₃ ' containing the same recurring structure asprecursor copolymer segment T₁ '. The precursor copolymer containingsegments T₁ '--M₂ '--T₃ ' is then hydrogenated to form hydrogenatedcopolymer of structure T₁ --M₂ --T₃.

The present invention relates to novel segmented hydrogenated copolymersof butadiene wherein the copolymer's chain contains at least onecrystallizable segment rich in methylene units and at least one lowcrystallinity segment relatively rich in substituted methylene units,wherein the low crystallinity copolymer segment is characterized in theunoriented bulk state after at least about 48 hours annealing at 23° C.by a degree of crystallinity of less than about 0.2% at 23° C., andwherein the copolymer's chain is intramolecularly heterogeneous. Thecrystallizable segments comprise an average of from about 20 to 90weight percent, preferably from about 25 to 85 weight percent, and morepreferably from about 30 to about 80 weight percent of the totalcopolymer chain, and contain an average 1,4-polybutadiene content whichis at least about 20 mole percent, preferably at least about 30 weightpercent. The low crystallinity copolymer segments comprise an average offrom about 80 to 10 weight percent, preferably from about 75 to 15weight percent, and more preferably from about 70 to 20 weight percentof the total copolymer chain, and have a 1,4-polybutadiene content notgreater than about 20 mole percent. The copolymers in accordance withthe present invention comprise intramolecularly heterogeneous chains,with substantially each chain containing both crystallizable and lowcrystallinity segments.

The hydrogenated copolymers of the instant invention have weight-averagemolecular weights (Mw) as low as about 2,000. The preferred minimum isabout 10,000. The more preferred minimum is about 20,000. The maximumweight-average molecular weight can be as high as 2,000,000. Thepreferred maximum is about 500,000. The more preferred maximum is about250,000. The M segments have a Mw of from about 1,000 to about1,000,000, preferably from about 10,000 to about 2,000,000, and morepreferably about 20,000 to about 100,000. The T segments have a Mw offrom about 1,000 to about 1,000,000, preferably about 5,000 to about200,000, and more preferably from about 10,000 to about 100,000. Theweight average molecular weights are determined by gel permeationchromatography (GPC) using tetrahydrofuran (THF) and light scattering asdiscussed above.

The copolymers of the instant invention have a molecular weightdistribution (Mw/Mn) of about 2.0 or less, preferably about 1.9 or less,and more preferably about 1.8 or less, as determined by SEC as discussedin G. Ver Strate, C. Cozewith, S. Ju, in Macromolecules, 21, 3360, 1988.

It is believed the novel copolymer's improved function as viscositymodifiers can be at least partially attributed to the ability of acontrolled portion of the copolymer's molecules to crystallize inoleaginous compositions such as lubricating oils at temperatures abovethe cloud point of the lubricating oil. This occurs both inter- andintra-molecularly.

Typical lubricating oil contains paraffinic and isoparaffinic waxycomponents which are capable of crystallizing. As the lubricating oil iscooled from high temperatures (above T_(c)), these waxy components beginto crystallize. When the crystals become large they scatter light andmake the oil turbid (the cloud point, T_(c)). Below the cloud point,waxes in the oil can co-crystallize with the crystallizable viscositymodifier crystallizable segments, effectively crosslinking the viscositymodifier polymer molecules, resulting in high "effective" polymermolecular weights, or causing "gelation" of the oil. This is observed bythe appearance of a yield stress upon shearing. Such effectively highmolecular weights are undesirable, as they increase the oil viscosity atlow temperatures making it difficult for the oil to be pumped or poured.

The associated copolymer molecules of this invention are believed tohave a smaller effective hydrodynamic volume per molecule than in theirunassociated state, which lowers the relative viscosity of thelubricating oil solution thereof and provides low formulated oilviscosities at low temperatures. It is believed the copolymer'scharacteristics of exhibiting a higher polymer association temperaturethan the oil's cloud point minimizes interaction with the wax in the oiland accordingly decreases the tendency of oils to undergo gelation.Also, only a portion of these copolymer molecules is crystallizableunder the use conditions. The non-crystallizable portion is believed toact as a steric barrier to help prevent excessive intermolecularassociation. The controlled segmented nature of the polymers isessential to their performance.

If the polymer has already associated above the cloud point temperature,the polymer and wax have little opportunity to interact. Furthermore, ifthe polymer contains segments which are low enough in methylene tocompletely avoid crystallization and are properly located along thecontour, these will act as steric blocks to wax or excessivepolymer/polymer interaction. Thus, two polymer characteristics areneeded: crystallization above the wax appearance temperature and asegmented structure to stabilize agglomeration before gels form.

The copolymers of the present invention are preferably prepared byanionic polymerization. This method of polymerization offers certainunique advantages which makes it extremely useful in the synthesis ofthe polymers of the present invention. In particular, by the use ofanionic polymerization, it is possible to obtain polymers having anarrow molecular weight distribution, to obtain tapered or blockpolymers, and to control the structure of the polymers derived fromconjugated dienes.

Unlike free-radical polymerization reactions, anionic polymerizationscan be performed where there is no facile chemical termination step. Ofcourse, termination reactions do occur, but under carefully selectedconditions with the monomers of the present invention, using inertsolvents and highly pure reactants, the end groups have indefinitelifetimes. The non-terminated chains derived from anionichomopolymerization can be used for the synthesis of block polymers bysequential addition of different monomers as described hereinbefore.Thus anionic polymerization offers flexibility in allowing either blockor tapered polymers to be readily produced. As mentioned hereinbeforepolymers with narrow molecular weight distribution having better shearstability than those with broader distributions can be produced. Shearstability is a desirable property in polymers used as viscosity indeximprovers.

Anionic polymerization generally offers a wider latitude of techniquesfor producing varied structures of conjugated diolefin polymers. Withbutadiene monomer, 1,4- and 1,2-addition can be regulated by theappropriate combination of reaction conditions, including catalyst,solvent type, and temperature. Hydrogenated precursor copolymerscontaining butadiene units predominantly in the 1,4-configuration aremuch more effective in increasing the V.I. than hydrogenated precursorcopolymers containing butadiene units predominantly in the1,2-configuration.

The polymers of the present invention can be prepared with knownmetallic and organometallic catalysts such as lithium metal or sodiummetal and organo-lithium or organosodium catalysts. Preferred lithiumcompounds are compounds containing two lithium atoms per compoundmolecule and include LiR^(L) Li wherein R^(L) is an organic compound,preferably a hydrocarbon having at least one carbon atom and preferablyfrom 3 to 6 carbon atoms. Useful dilithium (DiLi) compounds aredisclosed in A. F. Halasa et al. Organolithium Catalysis of Olefin andDiene Polymerization, Advances in Organometallic Chemistry, Vol. 18,pages 55-97, Academic Press, Inc. (1980). Suitable organo-lithiumcatalysts may be represented by the formula R² Li wherein R² is a C₃ toC₃₀, and preferably C₃ to C₁₀ alkyl, aralkyl, or cycloalkyl group.Specific examples of suitable catalysts include n-propyllithium,isopropyllithium, n-butyllithium, tertiarybutyllithium, n-decyllithium,benzyllithium, 4-phenyl-n-butyl-lithium, etc. Particularly preferred arethe butyl-lithiums, i.e., normal-, sec-, iso-, andtertiary-butyllithiums.

An inert diluent, in which the catalyst is soluble, may be employed. By"inert" it is meant that the diluent does not react, although the natureof the solvent may affect the relative amount of 1,2- and1,4-configuration that is obtained. The inert diluent will generally bea hydrocarbon free of olefinic unsaturation containing from 3 to 16carbon atoms. Suitable inert diluents include aliphatics, such asn-pentane, n-hexane, isooctane, n-nonane, etc.; alicyclics, such ascyclopentane, cyclohexane, cycloheptane, etc., aromatics such asbenzene, toluene, xylene, chlorobenzene, etc. The amount of diluentemployed in the preparation is not critical, except that sufficientamounts should be used to solubilize the amount of organolithiumcatalyst used. Generally, 0.5 to 200, preferably 1 to 50 liters of thediluent per gram mole of organo-lithium catalyst are employed during thepreparation of the polymer.

The amount of catalyst employed primarily depends upon the degree ofpolymerization desired. The term "degree of polymerization," as employedherein, means the total number of monomeric units present in thepolymer. Ordinarily, each mole of organo-lithium catalyst will generatea mole of polymer. Thus, "degree of polymerization" may be convenientlydefined by the generalization: ##EQU3##

Since to obtain the desired molecular weights, the average number ofmonomeric units in the polymer will generally be from about 500 to about10,000. About 0.0001 to 0.002 mole of organolithium catalyst per mole ofmonomer will ordinarily be utilized.

The polymerization reaction generally takes place at about -50° to about150° C., and preferably at 20° to 60° C. Reaction times as short as 1minute or as long as 75 hours may be employed. Preferably, thepolymerization reaction is carried out for from 4 minutes to 24 hours.Reaction pressure is not critical; pressures may range from atmosphericto super-atmospheric. Preferably for economy and ease of handling,atmospheric pressure is utilized.

In one embodiment the monomers are added sequentiallly whereby block orsegment copolymers may be obtained. For example in the preparation of acopolymer of structure III, i.e., T--M, one of the monomers, e.g.,butadiene, is polymerized in the presence of the catalyst via1,4-addition for a period of time, e.g., 2 hours, to form aunhydrogenated precursor copolymer segment M' containing at least about65 weight percent butadiene in the 1,4-configuration. Then theconditions of polymerization are changed for polymerization to takeplace through 1,2-addition. The comonomer forms 1,2-butadiene unitsresulting in unhydrogenated precursor segment T'. The segmentedcopolymer is then hydrogenated to form methylene rich segment M,corresponding to a 1,4-polybutadiene content of at least about 20 weightpercent, and substituted methylene rich segment T having a methylenecontent corresponding to 1,4-polybutadiene of less than about 20 molepercent.

A hydrogenated copolymer having structure IV, i.e., T₁ --M₂ --T₃, can beprepared by first polymerizing butadiene by 1,2-addition, to formunhydrogenated precursor segment T₁ ' containing predominantly1,2-butadiene units; the reaction conditions are changed and thebutadiene monomer is polymerized (in the presence of T₁ ') via1,4-addition mechanism to form unhydrogenated precursor segment M₂ 'containing at least about 20 mole percent of 1,4-configurationbutadiene; and then the reaction conditions changed to polymerize thebutadiene via 1,2-addition to form unhydrogenated precursor segment T₃ 'containing predominantly 1,2-butadiene. The segmented copolymer T₁ '--M₂'--T₃ ' is then hydrogenated to form the T₁ --M₂ --T₃ structure.

In the foregoing discussion concerning the preparation of copolymers ofstructures M--T and T₁ --M₂ --T₃ it is to be understood that the Msegment need not contain, and usually does not contain, only methyleneunits derived from the hydrogenation of 1,4-addition butadiene. It mayalso contain some substituted methylene units derived from thehydrogenation of the 1,2-addition butadiene so long as those substitutedmethylene units do not exceed about 80 mole percent of the total units.Likewise, segments T, T₁ and T₃ may contain, and usually do contain,methylene units derived from the hydrogenation of 1,4-additionbutadiene, so long as the total methylene units present in T, T₁ and T₃do not correspond to a 1,4-polybutadiene content exceeding 20 molepercent.

An alternate and preferred embodiment of the present invention is onewherein the copolymer is in a star polymer form, i.e., a star blockcopolymer. A living block copolymer having monomeric units derived from1,4-butadiene and 1,2-butadiene addition products of the polymerizationof butadiene is formed as recited above. The copolymer has the abovestructures of T--M and T₁ --M₂ --T₃. When the copolymer reaches adesired molecular weight a polyalkenyl coupling agent is introduced. Thepolyalkenyl coupling agent acts as a nucleus of the star. The livingpolymers react at one end with the polyalakenyl coupling agent. Theliving polymer is then deactivated or killed in a known manner. Each armof the star is thereby attached at one end to the nucleus with theopposite end preferably being a "T" segment. That is, the free ends ofthe arms of the star are preferably rich in substituted methylene unitsmaking them amorphous.

Each arm of the star preferably has the character of the straight chaincopolymer from which it forms. For the purposes of the present inventionthe term block copolymer will therefore include star copolymerscontaining arms which have blocks consistent with the straight chainblock copolymers recited above. Preferred molecular weights for starpolymers are higher than their linear counterparts.

Apart from the specific and improved character of the block copolymerstructure of the arms, the star polymers of the present invention aremade in accordance with procedures disclosed in patents such as U.S.Pat. No. 4,358,565 and U.S. Pat. No. 4,620,048. The improvement of thestar copolymer of the present invention being that it is a copolymerhaving arms wherein there are sharp blocks characterized by theiramorphous and crystalline properties. The configurations havingmethylene rich groups at the arms of the stars near the star center areuseful in lubricating oils which contain paraffin and isoparaffinic waxycomponents capable of crystallizing to prevent crystalline gelling.

More particularly, the star polymers of the present invention are madeby forming block copolymers as recited above. The block copolymers havea structure as presented in formulas III, and IV with the structure ofIV being most preferred. The living block copolymer is first prepared bycopolymerizing blocks of butadiene and isoprene as recited above.

In a preferred method the living block copolymers produced are reactedwith a polyalkenyl coupling agent such as a polyvinyl compound, orhalosilane compounds such as SiCl₄. Such polyalkenyl coupling agentscapable of forming star-shaped polymer are known and indicated to bedisclosed in polymers such as in U.S. Pat. No. 3,985,830.

The polyalkenyl coupling agent should be added to the living polymerafter the polymerization of the monomers is substantially complete,i.e., the agent should only be added after substantially all of themonomers (formulas I and II) have been converted to the living blockcopolymer.

The amount of polyalkenyl coupling agent added is preferably at least0.5 moles per mole of unsaturated living polymer. Amounts of from 1 to15 moles, preferably 1.5 to 5 moles are preferred. The amount which maybe added in two or more stages is usually such so as to convert at least80-85 weight percent of the living polymers into star-shaped polymers.

The reaction between the living polymer and the polyalkenyl couplingagent or nucleator can be carried out in the same solvent as thereaction to form the living polymer. The reaction temperature can alsobe varied from 0° to 150° C., and preferably 20° to 120° C. The reactionmay also take place in an inert atmosphere such as nitrogen underpressure of from 0.5 to 10 bars.

The star-shaped polymers prepared are characterized by having a densecenter nucleus of crosslinked polyalkenyl coupling agent and a number ofarms of substantially linear unsaturated polymers extending outwardlytherefrom. The number of arms may vary considerably, but is typicallyfrom 4 and 25, preferably from 5 to about 15, and most preferably from 5to 10 arms. It is reported that the greater number of arms employedimproves both thickening of the efficiency and shear stability of thepolymer since it is possible to prepare a viscosity index improvingmolecule having a high molecular weight (resulting in increasedthickening efficiency) without the necessity of successively long arms.

The star-shaped polymers, which are still living, may be deactivated orkilled in a known manner by the addition of a second compound whichreacts with the carbon-ionic end group. Examples of suitabledeactivators include compounds with one or more active hydrogen such aswater, alcohol, such as methanol, ethanol, isopropanol, 2-ethylhexanol,or carboxylic acids such as acetic acid, compounds with one activehalogen atom, such as chlorine atoms (benzyl chloride or fluoromethane),compounds with one ester group and carbon dioxide. If not deactivated inthis way, the living star-shaped polymers will be killed by thehydrogenation step. Before being killed, the living star-shaped polymersmay be reacted with further amounts of monomers, such as the same ordifferent dienes, or functional monomers.

The molecular weights of the star-shaped polymer to be hydrogenated mayvary between relatively wide limits. However, they are typically betweenmolecular weights from about 25,000 to 1,500,000, and preferably from100,000 to 500,000. The molecular weights are weight average molecularweights determined by gel permeation chromatography.

The hydrogenation of the polymers of the present invention is carriedout using conventional hydrogenation procedures. The polymer is dilutedwith an inert solvent, such as those previously mentioned, or in theoriginal polymerization medium, and the polymer solution andhydrogenation catalyst are added to a high pressure autoclave. Theautoclave is pressured with hydrogen to about 100 to 3,000 p.s.i.g., andthen heated to 50° to 220° C., (preferably 75° to 150° C.), for about0.1 to 24, preferably 1 to 24 hours (preferably 2 to 10 hours), whilemixing. The reactor is then depressurized, the catalyst removed byfiltering, and the hydrogenated polymer recovered from the solvent byconventional stripping procedures.

The hydrogenation catalyst will generally be used in an amount of 0.1 to20 weight percent based upon the weight of the polymer to behydrogenated. The specific amount of catalyst employed depends somewhatupon the specific catalyst used. Any material functioning as an olefinhydrogenation catalyst can be used; suitable catalysts include Raneynickel, platinum oxide, platinum on alumina, palladium or charcoal,copper chromate, nickel supported on kieselguhr, molybdenum sulfide, andthe like. The best hydrogenation results were obtained with Raneynickel, in large excess, at high temperatures and pressure. Co or Nicarboxylates reduced with aluminum alkyls can also be used.

Hydrogenation is carried out to remove the olefinic unsaturation presentin the precursor copolymer. Hydrogenation may be complete orsubstantially complete. By complete hydrogenation is meant that all ofthe olefinic bonds are saturated. By substantially completehydrogenation is meant that substantially all of the olefinicunsaturation is saturated. By substantially all olefinic unsaturation ismeant at least about 80%, preferably at least about 90% of the olefinicunsaturation and most preferably greater than 98%.

Another embodiment of the present invention is a tapered block orsegmented copolymer of the hydrogenated 1,2- and 1,4-butadiene. Atapered block or segmented copolymer according to this invention is acopolymer obtained by anionically copolymerizing in hydrocarbon solutionin, for example, a batch reactor a mixture containing butadiene monomerto form a precursor copolymer having at least 75 weight percent1,4-configuration of the 1,4-butadiene and then hydrogenating saidprecursor copolymer.

The anionic polymerization and subsequent hydrogenation conditions usedin the preparation of the tapered segmented or block copolymer aresubstantially the same as those described hereinbefore. Theweight-average molecular weights of these tapered segmented or blockhydrogenated copolymers are generally the same as those described above.

The weight percent of the butadiene present in the reaction mixture isthat which is effective to form a tapered segmented or block copolymerhaving at least one crystallizable segment and at least one lowcrystallinity segment. Generally this amount of butadiene is from about20 to about 90 weight percent. Additionally, the amount of the1,4-configuration butadiene present in the precursor copolymer must bean amount which is effective to form a crystallizable segment uponhydrogenation of the precursor copolymer. Generally, this amount is atleast about 20 mole percent.

The polymers can be recovered by procedures well known in the art. Forexample, polar materials, such as water or C₁ to C₅ alkanols can beadded to inactivate the catalyst. Preferably, the reaction is terminatedby dropping the reaction system into 2 to 10 volumes of methanolcontaining about 0.1 weight percent antioxidant. After termination ofthe reaction, the hydrocarbon solution is washed with water or dilutemineral acid. Alternatively, the active polymer solution can be treatedwith hydrated clays, such as natural Attapulgus clay, which functions toboth inactivate the catalyst and to chemically absorb the lithiumcomponent. The polymer may be recovered by filtering the resultantpolymer solution, drying if necessary, and stripping of remaining inertdiluent at elevated temperatures (e.g., 70° to 120° C.) and reducedpressures (e.g., 0.1 to 100 mm. Hg). For the isolation of highermolecular weight polymers steam stripping or precipitation withanti-solvents is preferred.

By controlling the ratio of 1,4- to 1,2-butadiene in the anionicpolymerization it is possible to obtain an effective wide range ofmethylene to substituted methylene ratio in the hydrogenated product.

When the polymerization of the dienes has been completed, the copolymerthus obtained can be hydrogenated either immediately or after recoveryto obtain the desired hydrogenated copolymers according to theinvention.

The present invention includes compositions comprising an oleaginousmaterial such as lubricating oil and at least one hydrogenated blockcopolymer as described. There can be a minor amount, e.g. 0.01 up to 50weight percent, preferably 0.05 to 25 weight percent, based on theweight of the total composition, of the hydrogenated copolymer producedin accordance with this invention can be incorporated into a majoramount of an oleaginous material, such as a lubricating oil orhydrocarbon fuel, depending upon whether one is forming finishedproducts or additive concentrates. When used in lubricating oilcompositions, e.g. automotive or diesel crankcase lubricating oil,copolymer concentrations are usually within the range of about 0.01 to10 weight percent, of the total composition. The copolymers of theinvention may be utilized in a concentrate form, e.g., from about 5weight percent up to about 50 weight percent, preferably 7 to 25 weightpercent oil, e.g., mineral lubricating oil, for ease of handling, andmay be prepared in this form by carrying out the reaction of theinvention in oil as previously discussed. The lubricating oils to whichthe products of this invention can be added include not only hydrocarbonoil derived from petroleum, but also include synthetic lubricating oilssuch as esters of dibasic acids; complex esters made by esterificationsof monobasic acids, polyglycols, dibasic acids and alcohols; polyolefinoils, etc. The hydrogenated copolymers of the present invention areparticularly useful as fuel and lubricating oil additives, particularlyas Viscosity Index improver lubricating oil additives.

The hydrogenated copolymers of the instant invention are oil-soluble,dissolvable in oil with the aid of a suitable solvent, or are stablydispersible therein. The terms oil-soluble, dissolvable in oil, orstably dispersible in oil as that terminology is used herein does notnecessarily indicate that the materials are soluble, dissolvable,miscible, or capable of being suspended in oil in all proportions. Itdoes mean, however, that the additives for instance, are soluble orstably dispersible in oil to an extent sufficient to exert theirintended effect in the environment in which the oil is employed.Moreover, the additional incorporation of other additives may alsopermit incorporation of higher levels of a particular copolymer hereof,if desired.

The copolymers are particularly useful in lubricating oil compositions,which employ a base oil in which these copolymers are dissolved ordispersed. Base oils suitable for use in preparing the lubricatingcompositions of the present invention include those conventionallyemployed as crankcase lubricating oils for spark-ignited andcompression-ignited internal combustion engines, such as automobile andtruck engines, marine and railroad diesel engines, and the like.Advantageous results are also achieved by employing the additives of thepresent invention in base oils conventionally employed in and/or adaptedfor use as power transmitting fluids such as automatic transmissionfluids, tractor fluids, universal tractor fluids and hydraulic fluids,heavy duty hydraulic fluids, power steering fluids and the like. Gearlubricants, industrial oils, pump oils and other lubricating oilcompositions can also benefit from the incorporation therein of theadditives of the present invention.

The above oil compositions may optionally contain other conventionaladditives, pour point depressants, antiwear agents, antioxidants, otherviscosity-index improvers, dispersants, corrosion inhibitors,anti-foaming agents, detergents, rust inhibitors, friction modifiers,and the like.

Corrosion inhibitors, also known as anti-corrosive agents, reduce thedegradation of the metallic parts contacted by the lubricating oilcomposition. Illustrative of corrosion inhibitors are phosphosulfurizedhydrocarbons and the products obtained by reaction of aphosphosulfurized hydrocarbon with an alkaline earth metal oxide orhydroxide, preferably in the presence of an alkylated phenol or of analkylphenol thioester, and also preferably in the presence of carbondioxide. Phosphosulfurized hydrocarbons carbons are prepared by reactinga suitable hydrocarbon such as a terpene, a heavy petroleum fraction ofa C₂ to C₆ olefin polymer such as polyisobutylene, with from 5 to 30weight percent of a sulfide of phosphorus for 1/2 to 15 hours, at atemperature in the range of about 66° to about 316° C. Neutralization ofthe phosphosulfurized hydrocarbon may be effected in the manner taughtin U.S. Pat. No. 1,969,324.

Oxidation inhibitors, or antioxidants, reduce the tendency of mineraloils to deteriorate in service which deterioration can be evidenced bythe products of oxidation such as sludge and varnish-like deposits onthe metal surfaces, and by viscosity growth. Such oxidation inhibitorsinclude alkaline earth metal salts of alkylphenolthioesters havingpreferably C₅ to C₁₂ alkyl side chains, e.g., calcium nonylphenolsulfide, barium toctylphenyl sulfide, dioctylphenylamine,phenylalphanaphthylamine, phosphosulfurized or sulfurized hydrocarbons,etc.

Other oxidation inhibitors or antioxidants useful in this inventioncomprise oil-soluble copper compounds. The copper may be blended intothe oil as any suitable oil-soluble copper compound. By oil soluble itis meant that the compound is oil soluble under normal blendingconditions in the oil or additive package. The copper compound may be inthe cuprous or cupric form. The copper may be in the form of the copperdihydrocarbyl thio- or dithio-phosphates. Alternatively, the copper maybe added as the copper salt of a synthetic or natural carboxylic acid.Examples of same thus include C₁₀ to C₁₈ fatty acids, such as stearic orpalmitic acid, but unsaturated acids such as oleic or branchedcarboxylic acids such as napthenic acids of molecular weights of fromabout 200 to 500, or synthetic carboxylic acids, are preferred, becauseof the improved handling and solubility properties of the resultingcopper carboxylates. Also useful are oil-soluble copper dithiocarbamatesof the general formula (RR,NCSS)_(n) Cu (where n is 1 or 2 and R and R,are the same or different hydrocarbyl radicals containing from 1 to 18,and preferably 2 to 12, carbon atoms, and including radicals such asalkyl, alkenyl, aryl, aralkyl, alkaryl and cycloaliphatic radicals.Particularly preferred as R and R, groups are alkyl groups of from 2 to8 carbon atoms. Thus, the radicals may, for example, be ethyl, n-propyl,i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-heptyl,n-octyl, decyl, dodecyl, octadecyl, 2-ethyl hexyl, phenyl, butylphenyl,cyclohexyl, methyl-cyclopentyl, propenyl, butenyl, etc. In order toobtain oil solubility, the total number of carbon atoms (i.e., R and R,)will generally be about 5 or greater. Copper sulphonates, phenates, andacetylacetonates may also be used.

Exemplary of useful copper compounds are copper CuI and/or CuII salts ofalkenyl succinic acids or anhydrides. The salts themselves may be basic,neutral or acidic. They may be formed by reacting (a) poly-alkylenesuccinimides (having polymer groups of Mn of 700 to 5,000) derived frompolyalkylene-polyamines, which have at least one free carboxylic acidgroup, with (b) a reactive metal compound. Suitable reactive metalcompounds include those such as cupric or cuprous hydroxides, oxides,acetates, borates, and carbonates or basic copper carbonate.

Examples of these metal salts are Cu salts of polyisobutenyl succinicanhydride, and Cu salts of polyisobutenyl succinic acid. Preferably, theselected metal employed is its divalent form, e.g , Cu⁺². The preferredsubstrates are polyalkenyl succinic acids in which the alkenyl group hasa molecular weight greater than about 700. The alkenyl group desirablyhas a Mn from about 900 to 1,400, and up to 2,500, with a Mn of about950 being most preferred. Especially preferred is polyisobutylenesuccinic anhydride or acid. These materials may desirably be dissolvedin a solvent, such as a mineral oil, and heated in the presence of awater solution (or slurry) of the metal bearing material. Heating maytake place between 70 and about 200° C. Temperatures of 110° C. to 140°C. are entirely adequate. It may be necessary, depending upon the saltproduced, not to allow the reaction to remain at a temperature aboveabout 140° C. for an extended period of time, e.g., longer than 5 hours,or decomposition of the salt may occur.

The copper antioxidants (e.g., Cu-polyisobutenyl succinic anhydride,Cu-oleate, or mixtures thereof) will be generally employed in an amountof from about 50 to 500 ppm by weight of the metal, in the finallubricating or fuel composition.

Friction modifiers serve to impart the proper friction characteristicsto lubricating oil compositions such as automatic transmission fluids.

Representative examples of suitable friction modifiers are found in U.S.Pat. No. 3,933,659 which discloses fatty acid esters and amides; U.S.Pat. No. 4,176,074 which describes molybdenum complexes ofpolyisobutenyl succinic anhydride-amino alkanols; U.S. Pat. No.4,105,571 which discloses glycerol esters of dimerized fatty acids; U.S.Pat. No. 3,779,928 which discloses alkane phosphonic acid salts; U.S.Pat. No. 3,778,375 which discloses reaction products of a phosphonatewith an oleamide; U.S. Pat. No. 3,852,205 which disclosesS-carboxyalkylene hydrocarbyl succinimide, S-carboxyalkylene hydrocarbylsuccinamic acid and mixtures thereof; U.S. Pat. No. 3,879,306 whichdiscloses N(hydroxyalkyl)alkenyl-succinamic acids or succinimides; U.S.Pat. No. 3,932,290 which discloses reaction products of di- (loweralkyl) phosphites and epoxides; and U.S. Pat. No. 4,028,258 whichdiscloses the alkylene oxide adduct of phosphosulfurizedN-(hydroxyalkyl) alkenyl succinimides. The disclosures of the abovereferences are herein incorporated by reference. The most preferredfriction modifiers are succinate esters, or metal salts thereof, ofhydrocarbyl substituted succinic acids or anhydrides andthiobis-alkanols such as described in U.S. Pat. No. 4,344,853.

Dispersants maintain oil insolubles, resulting from oxidation duringuse, in suspension in the fluid thus preventing sludge flocculation andprecipitation or deposition on metal parts. Suitable dispersants includehigh molecular weight polyalkenyl succinimides, the reaction product ofoil-soluble polyisobutylene succinic anhydride with ethylene amines suchas tetraethylene pentamine and borated salts thereof.

Pour point depressants, otherwise known as lube oil flow improvers,lower the temperature at which the fluid will flow or can be poured.Such additives are well known. Typically of those additives whichusefully optimize the low temperature fluidity of the fluid are C₈ -C₁₈dialkylfumarate vinyl acetate copolymers, polymethacrylates, and waxnaphthalene. Foam control can be provided by an antifoamant of thepolysiloxane type, e.g., silicone oil and polydimethyl siloxane.

Anti-wear agents, as their name implies, reduce wear of metal parts.Representatives of conventional antiwear agents are zinc dialkyldithio-phosphate and zinc diaryldithiosphate.

Detergents and metal rust inhibitors include the metal salts ofsulphonic acids, alkyl phenols, sulfurized alkyl phenols, alkylsalicylates, naphthenates and other oil soluble mono- and dicarboxylicacids. Highly basic (viz, overbased) metal sales, such as highly basicalkaline earth metal sulfonates (especially Ca and Mg salts) arefrequently used as detergents. Representative examples of suchmaterials, and their methods of preparation, are found in co-pendingSer. No. 754,001, filed Jul. 11, 1985, the disclosure of which is herebyincorporated by reference.

Some of these numerous additives can provide a multiplicity of effects,e.g., a dispersant-oxidation inhibitor. This approach is well known andneed not be further elaborated herein.

Compositions when containing these conventional additives are typicallyblended into the base oil in amounts which are effective to providetheir normal attendant function. Representative effective amounts ofsuch additives are illustrated as follows:

    ______________________________________                                                         Wt. %.   Wt. %                                               Additive         (Broad)  (Preferred)                                         ______________________________________                                        Viscosity Modifier                                                                              .01-12  .01-4                                               Corrosion Inhibitor                                                                            0.01-5   .01-1.5                                             Oxidation Inhibitor                                                                            0.01-5   .01-1.5                                             Dispersant        0.1-20  0.1-8                                               Pour Point Depressant                                                                          0.01-5   .01-1.5                                             Anti-Foaming Agents                                                                            0.001-3  .001-0.15                                           Anti-Wear Agents 0.001-5  .001-1.5                                            Friction Modifiers                                                                             0.01-5   .01-1.5                                             Detergents/Rust   0.01-10 .01-3                                               Inhibitors                                                                    Mineral Oil Base Balance  Balance                                             ______________________________________                                    

When other additives are employed, it may be desirable, although notnecessary, to prepare additive concentrates comprising concentratedsolutions or dispersions of the viscosity index modifying copolymers (inconcentrate amounts hereinabove described), together with one or more ofsaid other additives (said concentrate when constituting an additivemixture being referred to here in as an additive package) wherebyseveral additives can be added simultaneously to the base oil to formthe lubricating oil composition. Dissolution of the additive concentrateinto the lubricating oil may be facilitated by solvents and by mixingaccompanied with mild heating, but this is not essential. Theconcentrate or additive-package will typically be formulated to containthe viscosity index improving copolymer additive and optional additionaladditives in proper amounts to provide the desired concentration in thefinal formulation when the additive-package is combined with apredetermined amount of base lubricant. Thus, the products of thepresent invention can be added to small amounts of base oil or othercompatible solvents along with other desirable additives to formadditive-packages containing active ingredients in collective amounts oftypically from about 2.5 to about 90%, and preferably from about 5 toabout 75%, and most preferably from about 8 to about 50% by weightadditives in the appropriate proportions with the remainder being baseoil.

The additives of the present invention may be suitably incorporated intosynthetic base oils such as alkyl esters of dicarboxylic acids,polyglycols and alcohols; polyalpha-olefins, polybutenes, alkylbenzenes, organic esters of phosphoric acids, poly-silicone oils, etc.

The final formulations may employ typically about 10 weight percent ofthe additive-package with the remainder being base oil.

Accordingly, while any effective amount, i.e., viscosity index improvingeffective amount, of the additives of the present invention can beincorporated into the fully formulated lubricating oil composition, itis contemplated that such effective amount Be sufficient to provide saidlube oil composition with an amount of the additive of typically fromabout 0.01 to about 10, preferably 0.1 to 6.0, and more preferably from0.25 to 3.0 weight percent, based on the weight of said composition.

Low temperature properties of the lubricating oils of the presentinvention are evaluated by a number of significant tests: MRV (MiniRotary Viscometer), using a technique described in ASTM-D3829, measuresviscosity in centipoise and yield stress in Pascals. MRV is determinedat -25° C.

CCS (Cold Cranking Simulator), using a technique in ASTM-D2602, a highshear viscosity measurement in centipoises. This test is related to alubricating oil's resistance to cold engine starting.

TP1 cycle MRV-Determined by ASTM D4684. This is essentially the same asthe ASTM MRV noted above, except a slow cooling cycle is used. The cycleis defined in SAE Paper No. 850443, K. O. Henderson et al.

The copolymer of the present invention, when used to formulatelubricating oils, will lower the viscosity measured using the ColdCranking Simulator Test. At the same time, low TP-1 cycle MRV ismaintained or lowered. The thickening efficiency (TE) is improved andthe lube oil has high viscosity at high temperatures and low viscosityat low temperatures.

The following Example further illustrates the present invention. Unlessotherwise stated, all of said weight percents expressed herein are basedon active ingredient (a.i.) content of the additive, and/or upon thetotal weight of any additive-package, or formulation which will be thesum of the a.i. weight of each additive plus the weight of total oil ordiluent.

EXAMPLE

Thickening efficiency (T.E.) is defined as the ratio of the weightpercent of a polyisobutylene (sold as an oil solution by Exxon ChemicalCompany as Paratone® N), having a Staudinger molecular weight of 20,000,required to thicken a solvent-extracted neutral mineral lubricating oil,having a viscosity of 150 SUS at 37.8° C., a viscosity index of 105 andan ASTM pour point of O.F. (Solvent 150 Neutral) to a viscosity of 12.4centistokes at 98.9° C. to the weight percent of a test copolymerrequired to thicken the same oil to the same viscosity at the sametemperature. For linear polymers of a given methylene content, thethickening efficiency is approximately proportional to the 0.75 power ofthe weight-average molecular weight.

In this Example a polymer having crystallizable and non-crystallizablesegments is prepared from butadiene by controlling the relativeproportions of 1,2 butadiene and 1,4 butadiene, using a high vacuumpolymerization techniques. The experimental procedure is of the typedescribed in M. Morton, L. J. Fetters, Rubber Chem. Tech., 48, 359(1975).

500 grams of cyclohexane is charged to a 2 liter reaction flask. To thisis added 0.5 millimeters of dilithium isoprene oligomer initiator (DILI)sold by Lithcoa and 54 grams of butadiene. The mixture is allowed toreact to form a predominantly (1,4poly butadiene) at 24° C. for about 24hours.

Dipiperidylethane (DPE) from Reilly Tire and Chemical Co. or Aldrich isthen added as a modifier at 2:1 mole ratio based on Li, as discussed inA. Halasa, D. Schulz, D. Tate, V. Mochel, Adv. Organometallic Chem., 18,55, (1980). An additional 54 grams of butadiene is added and thepolymerization proceeds at about 0° C. for 48 hours to form a block ofpredominantly 1,2 poly butadiene and at each end of the (1,4polybutadiene) center block. The reaction is then terminated by addingdegassed methanol.

The polymer is hydrogenated by heterogeneous catalysis. The butadieneportion polymerized prior to the addition of the modifier issubstantially in the 1,4 configuration and is hydrogenated to acrystallizable polyethylene-like segment. The butadiene added in thepresence of the modifier is substantially in the 1,2-form, and becomes apoly(ethylene-butene)-like after hydrogenation and isnon-crystallizable.

Due to the use of the di-initiator the crystallizable segments areformed in the center M block with amorphous T end blocks of1,2-butadiene.

While exemplary embodiments of the invention have been described, thetrue scope of the invention is to be determined from the followingclaims.

What is claimed is:
 1. A process comprising the steps of:forming throughpolymerization, a precursor polybutadiene block copolymer comprising atleast one precursor crystallizable segment comprising 1,4-polybutadieneand at least one precursor low crystallinity segment of polybutadienewherein butadiene is added to the polymer chain as 1,4 butadiene and 1,2butadiene, the precursor block copolymer comprising at least 10 percentby weight precursor crystallizable segments, wherein polymerizationcomprises forming a segment comprising at least 70 mole percentbutadiene added as 1,2-butadiene: forming a 1,4-polybutadiene segment;and forming a segment comprising at least 70 mole percent butadieneadded as 1,2-butadiene; adding a coupling agent to form a precursor starblock copolymer; and substantially hydrogenating the precursorpolybutadiene star block copolymer to form a hydrogenated blockcopolymer, arms of which comprise at least 10 percent by weight of atleast one crystallizable segment comprised of methylene units and havingan average methylene content corresponding to a 1,4-polybutadienecontent of at least about 20 mole percent, and at least one lowcrystallinity segment comprised of methylene units and substitutedmethylene units and having an average methylene content corresponding toa 1,4-polybutadiene content of less than about 20 mole percent.
 2. Theprocess as recited in claim 1 wherein the star block copolymer has from4 to 25 arms.
 3. The process as recited in claim 2 wherein the starblock copolymer has from 5 to 15 arms.
 4. The process as recited inclaim 1 wherein the star block copolymer has a weight average molecularweight of from 100,000 to 500,000.